I have faced with issue while opening Avantfax web page but it can be consequence of installing httpd update:
Warning: Unknown: open(/tmp/sess_3ec229c4cb7b053749c6f68d047aa95a, O_RDWR) failed: Permission denied (13) in Unknown on line 0
Warning: Unknown: Failed to write session data (files). Please verify that the current setting of session.save_path is correct () in Unknown on line 0
I don’t think so, we are (almost) compliant with upstream configuration.
I rather like to add the php option you suggeted for this case inside the httpd conf file, then we can go with the new implementation suggest by @davidep here: Php.ini for NethServer 7